It is a requirement of selfpriming centrifugal pumps that the gas pocket present in the suction line be drawn off by suction as quickly as possible and be pushed out via the pressure line.
A pump having a smooth annular guide channel is disclosed in the text entitled "Stromungsmaschinen" by Pfleiderer and Petermann, Springer Verlag, New York (1972), page 316. The smooth annular guide channel has lateral rotational surfaces and one of the two lateral rotational surfaces is as a rule the cover disc which is mountable and demountable whereas the other rotational surface is the housing wall. The value of a smooth annular guide channel is dependent exclusively upon its radial extent and is not dependent upon whether it becomes wider or narrower toward the outside thereof.
German utility model registration DE-GM No. 75 34 163 discloses a centrifugal pump for pumping liquids mixed with gases wherein a guide body is mounted so as to be tangent-like to the impeller in the guide channel. The gas/liquid mixture is not adequately skimmed away from the impeller. This mixture remains for longer periods of time in the chamber of the impeller and becomes heated.
German published patent application DE No. 35 39 883 A1 discloses a selfpriming centrifugal pump in the form of a multi-stage embodiment wherein the last stage has a separation chamber associated therewith. At least one guide surface and a diffuser collector nozzle corresponding thereto are mounted in the lead apparatus in addition to a plurality of guide vanes. Only an inadequate return of water to the impeller takes place and therefore a flushing of air or gas into the impeller occurs. This condition is present because of the many guide vanes and the configuration of the guide surface with the diffuser collector nozzle.